Grip mechanism for testing machines



Sept. 21, 1948- R. 1. SANDERSON ET AL 2,449,955

GRIP MECHANISM FOR TESTING MACHINES Filed Jan. 9, 1947 3 SheetsShe,et l

INVENTEIRSZ p v R. l. SANDERSON ETAL 2,449,955

GRIP MECHANISM FOR TESTING MACHINES Filed Jan. 9,1947 5 Sheets-Sheet 2 ZZZ/325g 1905587 1. 54/105950 M/ fl/Gf/Vf E. 7P05TL 5,

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IP ME ESTING MACHIN INVEN 5:

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W/W'MQ/A 2% Patented Sept. 21 1948 U I STAT,

can" MEonAmsM FOR Tush-no MAoHI'Nes Robert I.

Sanderson, Gary,

and Eugene It. a

Trostle, East Gary, Ind.

Application January 9, 1941, Serial No;1v2 ,1,014'

4Claims. (01. 735-103) .1 This invention relates to grip mechanism for testing machines and more particularly to mechanism for operating wedge type grips in a tensile testing machine. I V I In testing machines nowin common use, the grips applied with the machine are not dependable at heavy loads such as 200,000 pounds. When the test specimen breaks the gripping mechanism cannot stand the jolt and the broken specimen and even parts of the machine are thrown around to make the operation of the machine hazardous. Certain improvements have been made which prevent the grips from being thrown from the machine, but the mechanism is complicated and requires considerable maintenance. The travel of the gripping jaws is limited and in case of overrun, something must break. In the present machines the mechanism is the weakest part and will break It is an objectof this invention to provide grip mechanism which is simplein construction and in which the grip is easily secured and released.

Another object is to provide a device in which the gripping mechanism'will float and the travel of the jaws is not limited.

Still another object isto provide a device in which means are provided to permit the parts thereof to be easily assembled.

These and other objects will be more apparent after referring to the following specification and attached drawings, in which:

Figure 1 is a side elevatlonal view partly in cross section, the part in section being taken on the line 1-1 of Figure 2; 1

"Figure 2 is a horizontal section on "the line 11-11 of Figure 1; i

:Figure 3 is a view taken on the line III-11!" of Figure:2 with the gripping jaws and shims removed; I

Figure 4 is a perspective view of one of the gripping jaws;

Figure 5 is a view similar to Figure 2, but showing the preferred embodiment of the invention;

Figure 6 is a sectional view taken on the line VI-VI of Figure 5; and

Figure 7 is a diagram showing the movement of the jaws.

Referring more particularly to the drawings, reference numerals 2 and 4 indicate the top and bottom crossheads of a tensile testing machine. The gripping mechanism in the top crosshead is the reverse of the bottom mechanism and therefore, only the bottom gripping mechanism will be described, it being understood that the top gripping mechanism is similar thereto. The

crosshead'fisprovided with a jaw hole 6 having sl'ots8 at one end and wedge surfaces ID on each side; Aslide rack plate I 2, having tongues I 4 fitting inyslots 8, is provided with rack teeth IE on eachv sideof the center line of the test piece T, the teethextending from the outside edge upwardly at an angle toward the center line of the test piece. Meshing with the teeth I6 are teeth I 8 arranged on a pair of opposed jaws 20, one jaw being on each side of the center line of the test piece. Each jaw is provided with a'gripping surface 22 on its inner side and a wedge surface 24 on the side opposite the gripping surface, the wedge surfaces 24 having the same taper as the wedge surfaces I0. The gripping surface 22 is shaped to correspond to the shape of the test piece. A shim 26 may be provided between each of the wedge surfaces I0 and the jaws 20. The jaw teeth l8 are cut away at 28 to permit a little extra spread of the jaws. The bottom of the sliding rack plate 12 is provided with an extension 30 which is connected to the piston rod 32 Man air cylinder 34. The connection between the extension 30 and piston rod 32 is easily broken and as shown consists of a pin 36 which passes through holes in the extension 30 and the bifurcated end 38 of the piston rod 32. r

In operation the jaws 20 are assembled symmetrically on the rack plate [2 with the teeth l6 and IS in mesh." The assembly is then fitted in the hole 6 of the testing machine head 4 with the tongues I4 fitting in the slots 8. The shims 2B are put in place and the piston 32 connected to the extension 30. I Air is introduced into the bottom of the cylinder'34 to move the rack plate l2 upward. This causes the jaws 20 to rise and since they are guided by the wedge surfaces 24, they will move inwardly to close the grip 40. In case one of the jaws tends to slip its grip on the test specimen, the opposite jaw moves relatively forward and the teeth l8 exerta pressureon teeth It of the rack plate I2 which will transmit the force to the opposite side where the teeth l6 will bear on the teeth I 8 of the opposite jaw and force it forward. This equalizing feature insures positive gripping of the specimen T.

While the mechanism will operate as described above, it is preferred to provide means for facilitating assembly of the parts of the gripping mechanism. For this purpose the jaw holes 6 are provided with a pair of slots 42 on the end thereof opposite the slots 8. A T-shaped partition 44 is provided between the slots 42 so that the adjacent ends of the slots 42 are reduced in width at 46. A filler plate 48 having a stop lug 50 at its upper 3 end is adapted to be inserted into each slot 42. The maximum width of slots 42 is such that a clearance 52 is provided between the teeth l6 and I8 when the jaws 20 are positioned against the back wall of slots 42.

With this arrangement the mechanism is assembled as follows:

The rack plate 12 is positioned in the slots 8 and one of the jaws 520 .is projectedinto-the jaw hole 6 with its narrow end foremost andthe side thereof opposite the teeth l8 positioned against the back wall of slot 42. reached its desired vertical position, it is vmoved toward the rack plate l2 to bring the teeth [6 and 18 into mesh. The filler plate 48is then dropped into the slot 42 and moved downwardly until the stop lug 50 rests on the top of crosshead thus holding the jaw 20 in place as shown'in Figurefi. The second jaw is then positioned in thersame manner and the shims or liner plates 26 are dropped into position, The ioperationtof the dc vice .isthen thesameas set ,iorthabove. With this V-arrangement vthedi11er plate 48 scan be removed and either jaw .20 can-be easily backed out of mesh with the rack plate :and withdrawn from the head without disturbing the .restiof the assembly.

Referring to the vector .vdiagramoi Figure 7, it will be seenthat as .thesliding rack plate .12 moves from point 54 to point .56 there will .be ,a horizontal movement of the jaws equal to the horizontal distance between points Y56 and 58. Since-the jaws .reston the inclined teeth liinthe inward movement also ca-uses the jaw to move upward onthe-slopaof the'teeth a distancerepresented by the vertical ,distancebetween points tfiand Thuait will beseen that the jaws move frompoint 354 to point 53 ,whcn therack plate moves from point at to point 5.6 The specimenis then gripped in the upper jawsand tension is applied to the test FPi-EQB inthe usual manner. After the initial grip is secured -joy movementof the --slidingrack plate 42, the ceases to function and assumes a floating p.osi t-ion during which it is practically free {from :all stresses. The-pull :Qf the'mach-ine andthewedg ing action of the jaws -,tightens and maintains the-grip tdur-ing theentite-l-oadi-ng-of the specimen. Thejaws are :free to overrundnboth direc-- tions so that-the :loa-d is always carried by the jaws and is not transferred to the mechanism. Air pressu eis maintained-inrthe cylinder 34-during the entire pulling of :the test specimen so that it acts :as ;:a pneumatic 16115111011 1'10 absorb the force pi the rebound when :the specimen breaks. 1

While twoembodimen-ts of ourinvention have been shown and descrihed, it will be apparent that other adaptations and modifications may be .made without departing from the scope DI the .zfol-lowing wclaims.

When the jaw 20 has We claim:

1. Grip mechanism for the test piece in a tensile testing machine comprising a pair of opposed jaws, one on each side of the center line of the test piece, a gripping surface on each jaw, a wedge surface on each jaw on the side opposite the gripping surface, corresponding Wedge surfaces on said machine, a sliding plate mounte'd in-said machine along one side ;of both of the jaws, each of the jaws havingt-eeth therein on the end adjacent the sliding plate, the

teeth in each jaw extending at an angle from its .wedg-e surface toward the plane of its gripping surface, the sliding plate having teeth therein :ineshingawith the teeth in the jaws, and means for-moving said sliding plate in a plane parallel to the axis of the workpiece.

'2. Grip mechanism for the test piece in a. tensile testing machine comprising a pair of opposed jaws, one on each side of the center line or the test pie aerippins surf-ace on each law, ,a wedge surface on ica-ch lawon the opposite the gripping surface, corresponding wedge surfaces on said machine, ia's hding-plate mounted in said rnachine along one side oibcth Qithe jaws-each of the jaws having teeth therein ion the :end adjacent the sliding plate, the teeth in each 1 j aw extending at an 1 angle iromits wedge surface toward-the plane of its gripping surface, the sliding plate having teeth therein meshing with the teeth in the jaws, and anal! cylinder .for movingsaicl sliding plate in a plane parallel to the axis :oi the workpiece.

v3,. (3rrip mechanism for the test piece .in .a

tensile testing machine as defined in claim i in which :-.a filler plate is provided in said :machine against the. jaws on the side oisaid jaws ,oppm

site thesliding plate.

4. Grip mechanism :for the test piece in a tensile :testing machine as-definedin claim 1 in (which a;pair-of slots are provided .in saidma chine on the side 1 of the jaws opposite the sliding plate, andazil-llelt plate is provided.ior eachslot, said filler plates being thicker-than the depth of the teeth in said jaws.

I .ROBERII' -l. .SANDERSQN.

:R.- TROS'ITLE.

fiEFERENGES- CITED The following references are of record in the' file of this patent:

UNITED STATES PATENTS 

